The S-P interval increases with increasing distance from the epicentre. Time it takes for P-waves and S-waves to travel through the Earth and arrive at a seismographic station.Īs we know that the P waves reach the to the seismographs first at a station, the difference between the time of P waves and S waves is called S-P Interval.

Recorded seismograph of the earthquake from at least three seismographic stations at different distances from the epicentre of the quake.To determine the location of an earthquake, the following two things of info are required: Role of Seismic waves in determination of Epicentre P-wave velocities are much slower in the outer core than in the deep mantle while S-waves do not travel at all in the liquid portion of the outer core. The above finding led to determine that mantle is denser than crust and is viscous, semi-molten material. It was later called Mohorovičić discontinuity or simply Moho. This was enough to conclude that there is something below earth crust which has a greater density and varied composition. This means that for a seismograph stations located at about 150 Kilometers from a shallow focus earthquake epicentre received those waves first which came from beneath the ground via mantle. In his observations, Mohorovičić found that when the focus of the Earthquake is not too deep, some waves are propagated along the surface and remains in the crust, while other set enters the mantle, speeds up and reaches the seismometer first. In earth crust their speed is around 2-8 kilometers per second, while in mantle the speed is up to 13 kilometer per second, because mantle is denser. The speed of the seismic waves varies with the composition of the medium. How Seismic waves help in defining Earth’s interior? Involve shear motion in a horizontal plane. They are a variety of S-waves where the particles of an elastic medium vibrate transversely to the direction of wave propagation, with no vertical components.

Love waves make the ground vibrate at right angles to the direction of waves. Behave like water waves with elliptical motion of material in wave. These are also called Rayleigh waves after Lord Rayleigh who first described these waves. L Waves or Surface Waves travel near the earth’s surface and within a depth of 30-32 kilometers from the surface. Rayleigh Waves and Love waves Rayleigh Waves or L-waves They have a medium wavelength and cause vibrations at right angles to the direction of propagation of waves.

The S waves only travel through solids because liquids and gases have no sheer strength. Secondary waves or Sheer waves or shock waves are transverse waves which create vibrations perpendicular to the direction of wave movement. They travel fast in denser, solid materials. They have shortest wavelength, fastest speed and can travel through solid, liquid and gas.

The Primary waves or Push waves are longitudinal / compression waves that vibrate parallel to the direction of wave movement. Rock elasticity increases faster than density with depth. In Body waves the speed decreases with increasing density of rock and increases with increasing rock elasticity.

Role of Seismic waves in determination of Epicentre.

How Seismic waves help in defining Earth’s interior?.

The seismac waves of an earthwuake